21172538 has 4 divisors (see below), whose sum is σ = 31758810. Its totient is φ = 10586268.

The previous prime is 21172537. The next prime is 21172561. The reversal of 21172538 is 83527112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 18292729 + 2879809 = 4277^2 + 1697^2 .

It is a super-2 number, since 2×21172538² = 896552730722888, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21172538.

It is not an unprimeable number, because it can be changed into a prime (21172537) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5293133 + ... + 5293136.

Almost surely, 2^21172538 is an apocalyptic number.

21172538 is a deficient number, since it is larger than the sum of its proper divisors (10586272).

21172538 is a wasteful number, since it uses less digits than its factorization.

21172538 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10586271.

The product of its digits is 3360, while the sum is 29.

The square root of 21172538 is about 4601.3626242669. The cubic root of 21172538 is about 276.6459438358.

The spelling of 21172538 in words is "twenty-one million, one hundred seventy-two thousand, five hundred thirty-eight".